Manufacture of aliphatic acids and their esters



Patented Get. 25, 1932 l -ATENT GFF'EQE HENRY DR EYFUS, OF LONDON,ENGLAND IiIANUFACTURE OF ALIPHATIC ACIDS AND THEIR ESTERS No Drawing.Original application filed March 8, 1929, Serial No. 345,441, and inGreat Britain March 16, 1928. Divided and Lie application filed June 24,1930. Serial No. 463,579.

- In a previous U. S. Patent application of "myself and W. Bader SerialNo. 188,116 filed September 1926, is described inter alia how aceticacid (in the free state or in the form of its methyl ester) maybeproduced by subjecting dimethyl ether and carbon monoxide to the actionof heat and pressure in the presence of inorganic acid catalysts, namelyinorganic acids or inorganic acids contaming an organic group, or acidsalts of such acids.

According to the present invention I have now found that methyl acetateand acetic acid can be prepared in a very satisfactory manner by causingdimethyl ether to react with carbon monoxide in the absence ofcatalysts. The reaction may if desired be performed under ordinaryatmospheric pressure but the reaction proceeds more rapidly under highpressures. The pressure may be, as high as -1- l00, 200 or 300'atmospheres or any higher pressure that can conveniently be attained inpractice.

The reaction may be performed at ordinary temperatures but it is greatlyaccelerated by elevated temperatures. I referably erform the reactionunder pressure (e. g. under pressure of to 300 atmospheres or more) attemperatures over 100 (1, e. g. from'about200 to e50 C. and preferablyat temperatures of from about 300 to 400 C.

In performing the invention I may employ carbon monoxide as such or inthe form of idustrial or other mixtures with hydrogen and/or inertgases, e. g. methane, nitrogen etc. Thus I may use water gas, producergas or coke oven gas, but it is preferable to use carbon monoxide alone.

The reaction may be performed in any suitable vessels for instancevessels made of or lined with copper or other metalsnot liable toproduce carbonyls by reaction with the carbon monoxide.

The carbon monoxide and dimethyl ether may be subjected to the reactioninany suitablemanner. Convenientlythe process may be carried out in acontinuous manner by mixing the carbon monoxide (or a gas containing.the same) with dimethyl ether vapour and passing the mixture into areaction chamber, the reaction chamber being heated to a tem perature ofabout 250 to 400 C. and preferably 300 to 400 C. but the invention isnot limited in this respect.

Or again, the dimethyl ether may be submitted to the reactioncontinuously with its production; thus for instance a mixture of methylalcohol and sulphuric acid may be heated in the known manner to producedimethyl ether and a regulated stream of carbon monoxide be run throughthe hot reaction mixture, whereby a mixture of carbon monoxide anddimethyl ether may be obtained and subjected continuously to thereaction of the present invention. For instance the mixture of carbonmonoxide and dimethyl ether so produced may be caused to pass throughcompressors or the like in which it is raised to the desired pressure(e. g. 70 to 150 atmospheres or more) and from thence through a reactionvessel heated to the desired temperature (e. g. 300 to 400 (1).

The reaction of the invention enables methyl acetate and/0r free aceticacid to be porduced according to the quantity of water present in thereaction, and according to the conditions obtaining. The presence ofwater favours the production of free acetic acid, whereas the absence ofwater (or presence of small quantities of Water) and the presence ofexcess of dimethyl ether favour the production of methyl acetate. Thusit is possible to direct the reaction to the production of methylacetate practically exclusively by using an excess dimethyl ether inpresence of little or no water. dimethyl ether is employed andsufficient water is present, acetic acid is obtained, While mixtures ofmethyl acetate and acetic acid in various proportions can be obtained inac cordancewith theconditions adopted.

If the. reaction is so conducted as to produce substantial quantities ofmethyl acetate, the methyl acetate may be easily saponified and Ifhowever no excess of worked up into acetic acid and methyl alcohol ordimethyl ether.

The process of the invention can be carried into effect in manydifferent ways.

According to one method of performing the invention, I may, for example,use a closed train of apparatus comprising a gas circulating pump, whichdrives the carbon monoxide or gas mixture containing carbon monoxidefirst through a mixing chamber, where dimethyl ether, or din'iethylether and'w'ater, may be incorporated with the gas in the form ofvapour. The resulting gaseous mixture then passes through a heatexchanger into the reaction chamber. The products issuing from thereaction chamber pass through the heat exchanger to a condenser providedwith a receiver in which the uncondensable gases are separated from theliquid products. The liquid products are withdrawn and the gases arereturned to the gas circulating pump. This circuit may be supplementedby pres sure gauges, traps for acid, preheaters, flow meters,temperature controls, and so on.

The different parts of the apparatus are preferably protected againstcorrosion by carbon monoxide and acetic acid. Thus, for example, it ispreferable to avoid the exposure of the gases to the action of iron inthe apparatus, although especial alloys that will not form iron carbonylcan be used with advantage. Parts of the apparatus in contact withacetic acid may be made of or lined with copper or other metal orsubstance not liable to attack by acetic acid, and, as will of course beunderstood, parts of the apparatus in contact with both acetic acid andcarbon monoxide should be made of or lined with a material (e. g.copper) capable of resisting the action of both substances.

The following examples serve to illustrate convenient methods ofexecution of the invention, it being understood that they are givensolely by way of illustration and are in no way limitative:

Example I A gaseous mixture of dimethyl ether and carbon monoxidecontaining a preponderance of dimethyl ether is passed under a pressureof 200-300 atmospheres through a copper lined reaction vessel heated to350 to 400 C. The products leaving the reaction vessel are condensed toseparate the acetic acid which is present almost completely in the formof methyl acetate.

Example I l A gaseous mixture of dimethyl ether, car bon monoxide andsteam, which mixture does not contain any substantial excess of dimethylether, is subjected to reaction precisely in the manner described inExample I. The products leaving the reaction zone are condensed toseparate the acetic acid which is present largely or entirely in theform of free acetic aci As before mentioned the reaction of theinvention enables methyl acetate and/ or free acetic acid to beproduced. In cases where the reaction is conducted to produce meth lacetate (or mixtures thereof with acetic acid and it is desired tosaponify the same to produce free acetic acid, such saponification mayconveniently be performed continuously with the reaction or otherwise.

For instance, the saponification may be performed by the processdescribed in the above mentioned U. S. application Serial No. 138,116and in U. S. patent application of W. Bader Serial No. 295,611 filed26th July, 1928, by which means the saponification of esters of organicacids can be performed in such manner as to produce free acids in ananhydrous condition. The said process con sists in effecting thesaponification by means of just the theoretical amount of water requiredfor the reaction, a strong minerai acid, e. g. phosphoric or sulphuricacid, being used as the saponifying agent.

The reaction proceeds according to the equation 2CH COOCH +H O+ QCHCOOH+ CH O dimethyl ether and the dimethyl ether so produced may ifdesired be submitted to the process of the present invention to producefurther quantities of acetic acid or methyl acetate. In such method ofsaponification it is preferred to use phosphoric acid as the saponifyingagent.

The reaction takes place at temperatures between about 150 and about 300(1., temperatures between 180 and 220 C. being especially advantageous.For instance at 200 C. the reaction proceeds rapidly, and results insubstantially a quantitative yield.

The more highly hydrated forms of phosphoric acid for instance,orthophosphoric acid and pyrophosphoric acid, are capable of supplyingthe water required for the saponification, being themselves at the sametime dehydrated to the form of metaphosphoric acid. It is thereforepossible to perform the reaction in a continuous manner, by continuouslyintroducing supplies of ester and water in the requisite proportionsinto the phosphoric acid, the phosphoric acid serving in effect as acarrier for the water.

The saponification may be carried out in any apparatus designed for theinteraction of gas and liquids, for example, wash towers, mixer,bubblers, etc.

The saponification of the methyl acetate may be carried out continuouslywith its production. Thus for instance a mixture of carbon monoxide anddimethyl ether vapour may be caused to react under pressure, and theproducts of reaction containing methyl acetate, preferably expanded tolower pressures, for instance atmospheric pressure, are

passed together with the requisite quantlty of steam through a chambercontaining phosphoric acid maintained at lower temperatures, for example180 to 250 C.

The acetic acid can be condensed, and the dimethyl ether, which isgaseous at ordinary temperatures can be returned for admixture withfurther quantities of carbon monoxide for conversion into acetic acid.

The methyl acetate may however be separated from the uncondensable gaseswith which it is mixed, and is converted by a separate operation intoglacial acetic acid and dimethyl ether.

By employing for the reaction of the present invention homologues ofdimethyl ether in place of dimethyl ether, homologous aliphatic acidsand/or their esters may readily be obtained. Thus, for instance,propionic acid and/ or ethyl propionate may readily be obtained byemploying diethyl ether. In extending the process to the treatment ofsuch higher ethers similar precautions should be observed as totemperature, pressure and the presence or absence of water.

What I claim and desire to secure by Letters Patent is 1. Process forthe manufacture of an alkacyl compound which comprises subjecting analiphatic ether of formula wl 2ml) 20 to the action of carbon monoxidein absence of catalysts.

2. Process for the manufacture of an acetyl compound which comprisessubjecting dimethyl ether to the action of carbon monoxide in absence ofcatalysts.

3. Process for the manufacture of an alkacyl compound which comprisessubjecting an aliphatic ether of formula (Ga 2ml) 20 to the action ofcarbon monoxide in absence catalysts at a temperature between 200 and450 C.

4. Process for the manufacture of an alkacyl compound which comprisessubjecting an aliphatic ether of formula (GH ZM) 20 to the action ofcarbon monoxide in absence of catalysts at a temperature between 200 and450 C. and under a pressure of at least 50 atmospheres.

5. Process according to claim 1 and wherein the reaction is performed inpresence of water vapour.

6. Process for the manufacture of an alkacyl compound which comprisessubjecting a gasleous mixture of an aliphatic ether of formu a watervapour and carbon monoxide to a temperature between 200 and 450 C. and apressure of at least 50 atmospheres in absence of catalysts.

7. Process for the manufacture of an acetyl compound which comprisessubjecting dimethyl ether to the action of carbon monoxide in absence ofcatalysts at a temperature between 200 and 450 C.

8. Process for the manufacture of an acetyl compound which comprisessubjecting dimethyl ether to the action of carbon monoxide in theabsence of catalysts at a temperature between 200 and 450 C. and under apressure of at least 50 atmospheres.

9. Process according to claim 2 and wherein the reaction is performed inpresence of water vapour.

10. Process for the manufacture of an acetyl compound which comprisessubjecting a gaseous mixture of dimethyl ether, water vapour and carbonmonoxide to a temperature between 200 and 450 C. and a pressure of atleast 50 atmospheres in absence of catalysts.

In testimony whereof I have hereunto subscribed my name.

HENRY DREYFUS.

